Microphones are ubiquitous on many devices used by individuals, including computers, tablets, smart phones, and many other consumer devices. Generally speaking, a microphone is an electroacoustic transducer that produces an electrical signal in response to deflection of a portion (e.g., a membrane or other structure) of a microphone caused by sound incident upon the microphone. To process audio signals generated by a microphone, microphones are often coupled to an audio system.
One type of microphone increasingly used in audio systems is a MEMS microphone. In a MEMS microphone, a diaphragm or membrane having an electrical capacitance may be formed on a semiconductor, such that sound pressure incident upon the capacitive element may be converted into an analog electrical signal indicative of such sound pressure. A MEMS microphone may include an intrinsic highpass filter set by a volume of air in the microphone, analogous to an electrical capacitance, and an acoustic leakage through the microphone membrane, analogous to an electrical resistance. Such intrinsic highpass filter may be characterized by a cutoff frequency f3 db at which an output power of the intrinsic highpass filter is less than half of its pass-band value (also known as a 3-decibel or 3-dB cutoff frequency). For example, a cutoff frequency f3 db of an intrinsic highpass filter may be given by f3 db=f0±Δf where f0 is a nominal cutoff frequency and Δf defines an error range by which an actual cutoff frequency may vary from the nominal cutoff frequency.
Specifications for MEMS microphones to be used in various applications may require smaller error ranges for the cutoff frequency than can be provided by MEMS microphones. For example, a MEMS microphone may have a cutoff frequency f3 db=35 Hz±10 Hz, but systems requirements for an electronic system comprising the MEMS microphone may have a requirement of a target cutoff frequency of ftarget=35 Hz±4.5 Hz. Accordingly, systems and methods for effectively reducing an error range of the cutoff frequency of a MEMS microphone's intrinsic highpass filter may be desirable.